a/ \(x\left(x^2-9\right)-\left(x^3+8\right)=0\)
\(\Leftrightarrow x^3-9x-x^3-8=0\)
\(\Leftrightarrow9x=-8\Rightarrow x=-\frac{8}{9}\)
b/ \(\left(x+2\right)\left(3-4x\right)-\left(x+2\right)^2=0\)
\(\Leftrightarrow\left(x+2\right)\left(3-4x-x-2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(1-5x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+2=0\\1-5x=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-2\\x=\frac{1}{5}\end{matrix}\right.\)
c/ \(2x^2-7x-4x+14=0\)
\(\Leftrightarrow2x^2-11x+14=0\)
\(\Leftrightarrow2x^2-4x-7x+14=0\)
\(\Leftrightarrow2x\left(x-2\right)-7\left(x-2\right)=0\)
\(\Leftrightarrow\left(2x-7\right)\left(x-2\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{7}{2}\\x=2\end{matrix}\right.\)
d/ \(3\left(x-5\right)=2x\left(x-5\right)\)
\(\Leftrightarrow2x\left(x-5\right)-3\left(x-5\right)=0\)
\(\Leftrightarrow\left(2x-3\right)\left(x-5\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=\frac{3}{2}\\x=5\end{matrix}\right.\)
